American physicist honoured with the Nobel Prize for Physics in 1923
for his study of the elementary electronic charge and the photoelectric
In 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron. He began by measuring the course of charged water droplets in an electrical field. The results suggested that the charge on the droplets is a multiple of the elementary electric charge, but the experiment was not accurate enough to be convincing. He obtained more precise results in 1910 with his famous oil-drop experiment, in which he replaced water (which tended to evaporate too quickly) with oil.
In 1916 he took up with similar skill the experimental verification of the equation introduced by Albert Einstein in 1905 to describe the photoelectric effect. He used this same research to obtain an exact value of Planck's constant.
In 1921 Millikan left the University of Chicago to become director
of the Norman Bridge Laboratory of Physics at the California Institute
of Technology (Caltech) in Pasadena, Calif. There he undertook a major
study of the radiation that the physicist Victor Hess had detected coming
from outer space. Millikan proved that this radiation is indeed of extraterrestrial
origin, and he named it "cosmic rays." As chairman of the
executive council of Caltech from 1921 until his retirement in 1945,
Millikan turned that school into one of the leading research institutions
in the United States.
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